FLUCTUATION-ASSISTED CRYSTALLIZATION IN IPP/PEOC POLYMER ALLOY
The new fluctuation-assisted mechanism for nucleation and crystallization in the isotactic polypropylene/poly(ethylene-co-octene) (iPP/PEOc) alloy which is a typical crystallizable and elastomeric polyolefin blend system has been studied. The growth kinetics of concentration fluctuations (a spontaneous spinodal process) implies that during liquid-liquid phase separation (LLPS) PP (and PEOc) rich domains gradually form and grow toward the liquid-liquid coexistent compositions. This process involves the (inter-)difrusion of PP chains toward PP-rich domains, and PEOc chains toward PEOc-rich domains. The moving PP (or PEOc) chains could induce some segmental alignment and orientation (relative to adjacent chains) during the reptative interdiffusion, as schematically illustrated in Figure la. These diffusion-induced aligned segments may attach themselves to the concentration gradient region (interface) and become nuclei or the precursor of nuclei for crystallization. For the late-stage phase separated PP/PEOc system, the LLPS assisted nucleation will happen mostly at the interface of the phase-separated domains as illustrated in Figure lb. In the denser iPP-rich domains, the nucleation requires to overcome higher free energy barrier, because the concentration have already reached the coexistent composition, which is far away from the initial concentration ψo, and the concentration fluctuations are too weak to assist nucleation for crystallization during the second temperature quench (to the crystallization temperature). The nucleation and crystallization may still be possible in these domains, but should be at a much slower nucleation rate because of the free energy barriers. Whereas, in the interface regions, the concentration is still near ψo and far away from the coexistent composition, so the spontaneous growth of concentration fluctuations and the chain alignments can still happen as shown in Figure 1c. Therefore, the nucleation and crystallization are much easier in the interface regions. This could be viewed as a new kind of heterogeneous nucleation and could be an addition to the regular nucleation and growth mechanism for crystallization.
Jiang Du Xiaohua Zhang Charles C.Han
State Key Laboratory of Polymer Physics and Chemistry, Joint Laboratory of Polymer Science and Materials, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
国际会议
PP’2010，Jinan International Symposium on Polymer Physics(2010济南国际高分子物理学术研讨会)
济南
英文
221-222
2010-06-06（万方平台首次上网日期，不代表论文的发表时间）